The present invention concerns a furniture drive comprising a drive unit which has an electric motor and a roller which is rotatable about an axis, wherein the roller has a surface for applying or winding up a flexible force transmission means.
Furniture drives with electric motors are already part of the state of the art. Thus, for example, WO 2007/147180 discloses a pull-in device for a drawer, wherein an electric motor rotates a roller by way of a drive unit and in so doing winds a pulling means on to the roller, whereby the drawer connected to the pulling means is pulled in the closing direction. A disadvantage of furniture drives of the general kind set forth is that the electric motors used can only provide the full torque, as from a certain rotary speed. That leads to problems when starting up and decelerating furniture parts, for example drawers, by means of a furniture drive of the general kind set forth.
The object of the invention is to provide a furniture drive having a simple device with which starting and deceleration of furniture parts moved with the furniture drive is facilitated.
That object is attained by a furniture drive having the features of the present invention. By virtue of a variable radial spacing in the direction of rotation of the surface of the roller, on to which a flexible force transmission means is applied or wound, a control cam is provided for the force transmission means. By virtue of that control cam, it is possible to targetedly control the necessary torque that the furniture drive must apply by way of the force transmission means for moving the furniture part. If, for example, the radial spacing of the surface and thus the radial spacing of the control cam is slight, the torque to be applied is also low. In that way, the electric motor can more rapidly provide its optimum rotary speed and thus its full torque.
In a particularly preferred embodiment of the invention, the roller itself is driven by the electric motor. Due to the above-specified measure, a lower torque is initially necessary to move the furniture part, whereby generally the motor power or the size of the motor of the furniture drive can be reduced.
It is particularly advantageous for the control cam to be designed in such a way that, at the beginning of the movement, the radial spacing of the control cam relative to the axis of rotation is kept at a minimum and then slowly increases until it reaches a maximum radial spacing. That measure means that the motor can more quickly reach its optimum rotary speed. In addition, it may be advantageous that, in the further configuration of the control cam, by way of which the force transmission means is caused to bear against or is wound on to a surface, the radial spacing relative to the axis of rotation of the roller is kept constant. It can be provided in that respect that the winding length corresponds to the length of the force transmission means, for example a cable or belt.
Particularly advantageous configurations for the control cam, are for example, spiral control cams, where the rate of increase in the radial spacing is constant, eccentric control cams, or the like.
In an embodiment of the invention, the rate of increase at which the radial spacing changes in the configuration of the control cam can be not constant, in contrast to a spiral control cam. It can be advantageous in that respect that the rate of increase in the radial spacing is particularly great at the beginning of the control cam, and then decreases in the further course of the control cam. It can, however, also be provided that the rate of increase in the radial spacing of the control cam increases in the course of the control cam or that the radial spacing at the beginning of the control cam has a low rate of increase, then increases more greatly in the further course of the control cam and again has lower rates of increase in a subsequent region of the control cam.
A particularly preferred embodiment of the invention provides that the radial spacing of the control cam in a first region increases from a minimum value to a maximum value and remains constant in a second region following the first region. That complies with the construction of a furniture drive according to the invention, especially as torque control is necessary only at the beginning of a change in motion (that is to say, for starting and decelerating the furniture part), while for the major part of the movement the constant torque that is prevailing after the attainment of a certain rotary speed of the electric motor is fully sufficient. In addition, such a control cam with a second region involving a constant radial spacing can avoid the roller which is rotatable about an axis becoming too large and no longer being suitable for installation in a furniture carcass.
In a preferred embodiment of the invention, that control cam is formed at an end of the roller. It can, however, also be possible for the control cam to be provided at the peripheral surface of the roller. That is the case, in particular, when the force transmission means is not wound around the roller a plurality of times.
As when starting the movement, when a furniture part to be moved has to be accelerated, major forces are also necessary when decelerating a moving furniture part. Therefore, at least one second control cam separate from the first can be provided on the roller. In that respect, the second control cam can have an opposite configuration to the first control cam. That is the case, for example, when the control cam is provided by the radial spacing of the surface, at which the force transmission means is applied or wound on, decreasing from a maximum value to a minimum value. In that case, during a motion of the furniture part in one direction, the force transmission means can be wound on or applied at a first control cam while it is unwound or removed at a second control cam. In that respect, less torque is necessary initially in the starting procedure by the first control cam while upon deceleration of the furniture part more force is made available by the second control cam. In other words, support in acceleration occurs at the first control cam at the beginning of the motion of the furniture part, which makes it easier for the electric motor. At the other control cam, there is support for deceleration towards the end of the motion of the furniture part, so a damping action is involved. In a motion in the reverse direction, that support in respect of deceleration and acceleration takes place at the respective other control cam.
It may be advantageous in that respect for the two control cams to be provided at the same end or at the opposite ends of the roller. It may be provided that a mutually opposite control cam is provided on both ends of the roller. On the other hand, it may also be advantageous to provide the same control cams at both ends, that is to say for example two respective mutually opposite control cams. The advantage of this is that the arrangement of the ends is immaterial, when fitting the roller.
In a further embodiment, control cams involving different torque configurations are implemented at the two opposite ends. In that case, two mutually opposite control cams can be arranged for example at each end. The control cams which are arranged at the two ends can differ in their rate of increase in the radial spacing from the axis of rotation of the roller.
As already mentioned, the force transmission means can be implemented by a cable or a belt. The force transmission means can be fixed with at least one end to the roller. The force transmission means can also be fixed with two ends to the roller. That is particularly advantageous in the case of two mutually opposite control cams. During start-up, the force transmission means is rolled on from its first end and unrolled from its second end.
Further advantageous configurations of the invention are described below.